Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Salaries and wages	$ 82,900	$ 54,338
Federal excise and other passenger taxes and fees payable	60,604	42,036
Aircraft maintenance	59,805	33,033
Airport obligations	52,029	56,299
Fuel	25,368	25,171
Interest payable	18,086	11,384
Aircraft and facility lease obligations	15,149	16,992
Other	25,736	23,117
Other current liabilities	$ 339,677	$ 262,370	$ 226,011